1. Field of the Invention
The present invention relates to a multilayer wiring board, a semiconductor device mounting board using such a wiring board, and a method of manufacturing such a multilayer wiring board.
2. Description of the Background Art
In recent years, the trend towards increased miniaturization and functionality of electronic equipment has produced a growing demand for higher density mounting of electronic components on the mounting boards used for mounting such electronic equipment. In order to enable these electronic components to be mounted on the mounting boards with higher densities, there are calls not only for further miniaturization of the electronic components, but also for finer and higher precision wiring processing on the printed wiring boards.
On the other hand, in order to ensure a minimal environmental impact, these days it is also necessary to consider the recycling of the aforementioned mounting boards. Consequently, wiring boards comprising a thermoplastic resin as a primary material have been attracting considerable attention.
These wiring boards use a highly heat resistant thermoplastic resin known as super engineering plastic, and not only enable finely detailed, high precision wiring processing, but also offer a number of other advantages including a high degree of mechanical strength, superior electrical insulation, and comparative ease of recycling. As a result, in order to meet the demands for increased wiring density, considerable research is being conducted into the use of highly heat resistant thermoplastic resins as the substrate materials for printed wiring boards.
Examples of thermoplastic resins which are used as these substrate materials include liquid crystal polymers and thermoplastic polyimides.
Furthermore, in a printed wiring board using one of these thermoplastic resins, a predetermined wiring circuit is formed on top of the printed wiring board in a similar manner to a conventional general purpose printed wiring board, namely using a so-called wet process in which copper foil is laminated on top of the printed wiring board, and the copper foil is then subjected to etching treatment using wet etching or the like to form the wiring pattern.
Other methods of forming the wiring circuit on the printed wiring board include methods in which the wiring circuit is formed by a dry process.
In these methods, screen printing techniques or dispensing techniques are used to print a conductive paste onto the printed wiring board in a predetermined wiring pattern, and this conductive paste is then subjected to heat treatment to complete the formation of a predetermined wiring circuit on the printed wiring board.
This method of printing on a conductive paste does not require the wet etching process used in conventional copper foil etching methods, and consequently the manufacturing process can be converted to a dry process, which offers the advantage of being even gentler on the environment.
The thermoplastic resin enables a shortening of the process tact, and also offers the advantages of superior moldability and plasticity, and is consequently considered a very favorable material as a board substrate material.
However, although conventional highly heat resistant thermoplastic resins offer advantages as highly heat resistant substrate materials, when the thermoplastic resin is laminated and integrated into a single unit, the resin must be heated to a temperature close to the resin melting point to ensure thermal fusion, and a problem arises during this heating and thermal fusion in that a resin flow, resulting from the large reduction in the modulus of elasticity at temperatures near the melting point, may cause distortions in the conducting material which forms the wiring circuit.
In addition, conventional printed wiring board production lines are suited to high volume low mix production, and consequently there is tendency for the production facilities to increase in size. Furthermore, chemical etching (wet etching) and plating techniques are typically used during the formation of wiring circuits on the printed wiring boards, and these techniques are undesirable from the viewpoint of environmental impact.
Furthermore as described above, examples of methods for wiring formation using dry processes include screen printing methods and dispensing methods using a conductive paste, although in both of these methods, there is a limit to the improvements in detail and precision of the conductive wiring which can be achieved in order to try and meet the ever increasing demands for higher density mounting.
In addition, as described above, in a laminated product of a thermoplastic resin on which a wiring circuit has been formed using a conductive paste, the resin must be heated to a temperature close to the melting point and subjected to pressure to fuse the thermoplastic resin layers together to create a single integrated unit, and as the pitch of the wiring becomes finer, distortion of the wiring resulting from resin flow during lamination is increasingly becoming a factor which cannot be ignored in substrate design.